[C] explode()

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>

struct v {
void *p;
size_t n;
};

struct v **explode(const void *p, const void *q, size_t pn, size_t qn, size_t size);
void *memmem(const void *p, const void *q, size_t pn, size_t qn, size_t size);
void *memdup(const void *p, size_t n);

int main(void) {
struct v **p = explode("a b", " ", 3, 1, 1);
struct v **q = p;
if(p == NULL) {
perror(NULL);
return EXIT_FAILURE;
}
while(*p) {
fwrite((*p)->p, 1, (*p)->n, stdout);
putchar(' ');
p++;
}
putchar('\n');
p = q;
while(*p != NULL) {
free((*p)->p);
free(*p++);
}
free(q);
return 0;
}

struct v **explode(const void *p, const void *q, size_t pn, size_t qn, size_t size) {
void *tmp;
struct v **rv = NULL;
size_t i;
ptrdiff_t j;
pn *= size;
qn *= size;
for(i = 0;; i++) {
while(pn >= qn && memcmp(p, q, qn) == 0) {
p = (char *)p + qn;
pn -= qn;
}
if((tmp = realloc(rv, (i + 1) * sizeof *rv)) == NULL) {
while(i--) {
free(rv[i]->p);
free(rv[i]);
}
free(rv);
return NULL;
}
rv = tmp;
rv[i] = NULL;
if(pn == 0) break;
if((rv[i] = malloc(sizeof **rv)) == NULL) {
while(i--) {
free(rv[i]->p);
free(rv[i]);
}
free(rv);
return NULL;
}
if((tmp = memmem(p, q, pn, qn, size)) == NULL) {
if((rv[i]->p = memdup(p, pn)) == NULL) {
while(i--) {
free(rv[i]->p);
free(rv[i]);
}
free(rv);
return NULL;
}
rv[i]->n = pn;
break;
}
else {
j = (char *)tmp - (char *)p;
if((tmp = memdup(p, j)) == NULL) {
while(i--) {
free(rv[i]->p);
free(rv[i]);
}
free(rv);
return NULL;
}
rv[i]->p = tmp;
rv[i]->n = j;
p = (char *)p + j;
pn -= j;
}
}
if(rv[i] != NULL) {
if((tmp = realloc(rv, (i + 2) * sizeof *rv)) == NULL) {
i++;
while(i--) {
free(rv[i]->p);
free(rv[i]);
}
free(rv);
return NULL;
}
rv[i + 1] = NULL;
}
return rv;
}

void *memdup(const void *p, size_t n) {
void *rv = NULL;
if((rv = malloc(n)) != NULL) memcpy(rv, p, n);
return rv;
}

void *memmem(const void *p, const void *q, size_t pn, size_t qn, size_t size) {
for(; pn >= qn; p = (unsigned char *)p + 1, pn -= size)
if(memcmp(p, q, qn) == 0) return p;
return NULL;
}

>>20
You can also take into account the fact realloc is probably doing that itself. In implementations where realloc doesn't do this by itself you are left wondering if your code should (why would you know better than the libc implementers?).